 ;; proper temporal comparison of two unrelated datasets.
 
 (ns forma.date-time
-  (:use [clj-time.core :only (now epoch date-time year month
-                                  plus in-msecs in-minutes
-                                  interval)]
+  (:use [clj-time.core :only (date-time month year)]
         [clj-time.format :only (unparse formatters)]
         [clojure.string :only (split)]
-        [clojure.contrib.math :only (ceil)]))
+        [clojure.contrib.math :only (ceil)])
+  (:require [clj-time.core :as time]))
 
 ;; ### Reference Time
 ;;

  in span-sized groups of unit (months or julians). [unit span] could be
  [julian 16], for example."
  [unit span start end]
  (let [[years units] (map #(delta % start end) [year unit])]
    (+ (* years (per-year unit span))
       (quot units span))))


                          "32" months
                          "16" sixteens
                          "8" eights)]
    (period-func (time/epoch) date)))

(defn datetime->period
  "Converts a datestring, formatted as `YYYY-MM-DD`, into an integer
